Evaluation of impact-induced traumatic brain injury in the Göttingen Minipig using two input modes.

OBJECTIVES: Two novel injury devices were used to characterize impact-induced traumatic brain injury (TBI). One imparts pure translation, and the other produces combined translation and rotation. The objective of this study was to evaluate the neuropathology associated with two injury devices using proton magnetic resonance spectroscopy (1H-MRS) to quantify metabolic changes and immunohistochemistry (IHC) to evaluate axonal damage in the corpus callosum. METHODS: Young adult female Göttingen minipigs were exposed to impact-induced TBI with either the translation-input injury device or the combined-input injury device (n=11/group). Sham animals were treated identically except for the injury event (n=3). The minipigs underwent 1H-MRS scans prior to injury (baseline), approximately 1 h after injury, and 24 h post injury, at which point the brains were extracted for IHC. Metabolites of interest include glutamate (Glu), glutamine (Gln), N-acetylaspartate (NAA), N-acetylaspartylglutamate (NAAG), and γ-aminobutyric acid (GABA). Repeated measures analysis of variance with a least significant difference post hoc test were used to compare the three time points. IHC was performed on paraffin-embedded sections of the corpus callosum with light and heavy neurofilament antibodies. Stained pixel percentages were compared between shams and 24-h survival animals. RESULTS: For the translation-input group (27.5-70.1 g), 16 significant metabolite differences were found. Three of these include a significant increase in Gln, both 1 h and 24 h postinjury, and an increase in GABA 24 h after injury. For the combined-input group (40.1-95.9 g; 1,014.5-3,814.9 rad/s2; 7.2-10.8 rad/s), 20 significant metabolite differences were found. Three of these include a significant increase in Glu, an increase in the ratio Glu/Gln, and an increase in the ratio Glu/NAAG 24 h after injury. The IHC analysis revealed significant increases in light and heavy neurofilament for both groups 24 h after injury. CONCLUSIONS: Only five metabolite differences were similar between the input modes, most of which are related to inflammation or myelin disruption. The observed metabolite differences indicate important dissimilarities. For the translation-input group, an increase in Gln and GABA suggests a response in the GABA shunt system. For the combined-input group, an increase in Glu, Glu/Gln, and Glu/NAAG suggests glutamate excitotoxicity. Importantly, both of these input modes lead to similar light and heavy neurofilament damage, which indicates axonal disruption. Identifying neuropathological changes that are unique to different injury mechanisms is critical in defining the complexity of TBI and can lead to improved prevention strategies and the development of effective drug therapies.

Techniques for the investigation of traumatic brain injury mechanisms characterized by magnetic resonance spectroscopy.

In the United States, traumatic brain injury (TBI) continues to be a leading source of death and disability, being responsible for 30.5% of all injury-related deaths [1]. Uncertainty still exists concerning the mechanisms and injury cascades involved. This study seeks to address many of the unknowns and criticisms of previous research. This study is focused on determining short term TBI development by finding a relationship between input accelerations and neuronal damage characterized by magnetic resonance spectroscopy (MRS) in an in vivo Göttingen minipig model. An injury device was designed and fabricated to impart rotational acceleration in the median plane of the animal using an articulated pendulum. Injury to the animal is caused by abrupt deceleration of the entire animal when the pendulum impacts brass tubes, which is repeatable. The animals (n=9) undergo baseline 7T MR scans prior to injury, immediately post-injury, and twenty-four hours post injury. MRS is performed on a voxel placed in the genu of the corpus callosum. Relevant metabolites include glutamate, N-acetylaspartate, myoInositol, creatine, and lactate. No clear trends were found for any of the metabolites for either time point. Further testing needs to be done in order to see the meaning of the metabolite differences in terms of underlying damage characterized by immunohistochemistry. This will give us insight into the meaning of using a noninvasive technique like MRS to look at TBI severity immediately post injury. Future work will include extending this study to define long term TBI development according to metabolite concentrations.